This invention relates to sheet-form fastening members of synthetic resin and to methods and machines for their manufacture.
An important aspect of the invention concerns hook fastener members for hook and loop fastening. These are formed of synthetic resin in running lengths. Typically there are multitudes of fastener elements, i.e. hundreds or even thousands of discrete hook elements per square inch. These are typically arranged in neat rows in the machine direction, i.e. in the direction in which the forming system produces the product.
These hook elements stand discretely from at least one side of an integral web-form base. The base forms the means of attachment of the fastening member to the article that carries it.
Fastener members with fields of such hooks typically have a pleasing, uniform, commercially acceptable appearance and are widely found in consumer and industrial products.
In a preferred method of manufacture, molding rolls are used in the process shown e.g. in Fischer U.S. Pat. No. 4,794,028. This process produces hook fasteners of commercial appearance in which the rows of hooks are straight and the spacing between the hook elements in both directions is regular.
Mold rolls for forming preferred fastening members of this kind typically comprise a series of thin circular plates, with mold plates alternating with spacer plates. Peripheries of the individual molding plates are machined with cutouts to define small hook profile cavities. The group of plates is held so their peripheries cooperate to define the surface of the roll. Because a large number of such plates is required and the plates must be carefully held in alignment, such mold rolls have been expensive to produce and maintain and have typically been confined to short lengths. The width of the product produced has been correspondingly restricted.
Conventional fastener materials produced in this way have been less than one or two feet in width and have had a web thickness between the hooks greater than 0.005 inch, typically 0.008 inch or more. Typically, in this method of manufacture, the hooks face in the machine direction or in the opposite direction, with the consequence that their major peel and shear strengths have been similarly oriented.
Other advantages and features will be apparent from the following description and claims.
We have discovered that it is possible to achieve a commercially acceptable sheet-form fastener member of synthetic resin in which the web or base portion lying between the multitude of fastener elements exists in a laterally permanently stretched condition, in many instances the substance of the web having molecular orientation at least partially in the direction of lateral stretch.
We have found that, while preserving the identity and functional shape of integral discrete fastener elements, the web portions between neighboring fastener elements can be stretched to a uniform thickness across the width of the product. In desirable instances, the web portions between the fastener elements are reduced to film thicknesses, and the resulting fastener member is readily conformable about curved or complex surfaces or is otherwise usefully applied to broad areas in an economical manner.
According to one important aspect of the invention a method of producing a sheet-form fastener product comprises the steps of: (1) lengthwise stretching a sheet of heat-softened synthetic resin to pre-orient the molecular structure of the sheet in a longitudinal direction; (2) with a rotating mold roll, molding from the sheet a running web having a base and a multiplicity of discrete fastener elements integral with the base and protruding from at least one side of the base; and (3) thereafter, under conditions in which the web is permanently stretchable, stretching the web widthwise in a manner that permanently stretches the base and increases the widthwise spacing of the fastener elements.
In some particularly useful embodiments, the fastener elements comprise touch-fastener hooks or the like.
Advantageously, in preferred embodiments, the widthwise molecular orientation and peel strength of the fastener product are increased during the widthwise stretching process.
In the presently preferred configuration, the ratio of the final width of the product to the original width of the product before widthwise stretching is between about 2 to 1 and about 10 to 1, and the widthwise stretching reduces the thickness of the base of the web by at least 50%.
In certain configurations, the widthwise stretching widens the web by at least 200% and reduces the thickness of the base of the web between fastener elements by at least two thirds.
In another embodiment, the method also comprises heating the web to render the base of the web permanently stretchable without detrimental change in the shape of the fastener elements. In certain arrangements, the fastener elements protrude from only one side of the web and the web is heated predominantly from a side opposite the side having the fastener elements.
In some examples, the resin is a thermoplastic resin suitable for forming hooks, comprising polypropylene, polyethylene, polyester, polystyrene, PVC, nylon or copolymers or polymer blends thereof.
In certain advantageous configurations, the widthwise stretching process causes molecular orientation and strengthening of the base of the web between fastener elements as it is stretched, such that as a result the base of the web between fastener elements is stretched widthwise substantially uniformly throughout.
In certain situations in which the synthetic resin has a Characteristic Minimum Stretch Ratio, the mold roll defines fastener elements and other stretch-limiting features over the area of the web, according to a predetermined pattern. The pattern is selected such that the ratio of the width of the final web to the width of the web before widthwise stretching is substantially less than the Characteristic Minimum Stretch Ratio. In certain useful embodiments, the fastener elements and stretch-limiting features resist local stretching of the web. In some situations, the stretch-limiting features are physical features of the product formed of synthetic resin integral with the base of the web, with the method including the step of differentially heating the web being formed such that the fastener elements and the stretch-limiting features are rendered less stretchable than the base of the web.
In some configurations, the temperature of the web base is controlled as the web is stretched widthwise. For instance, the fastener elements may be immersed in a temperature-controlled liquid during the widthwise stretching. In other instances, the web base is immersed in a temperature-controlled liquid during the widthwise stretching, or the web base is heated in a heated liquid bath during the widthwise stretching while leaving the fastener elements exposed to air.
In some embodiments a dual stretch process is employed, in which the step of stretching the web widthwise includes stretching the web widthwise in a first stretch zone, maintaining the web at an intermediate, stretched width, and then further stretching the web widthwise in a second stretch zone. Preferably, the rate of widthwise stretching varies along the first stretch zone.
In another aspect of the invention, a method is provided for producing a sheet-form fastener product, comprising (1) forming from synthetic resin a running web having a multiplicity of rows of discrete fastener elements integral with and protruding from at least one side of base of the web, the elements facing in a substantially longitudinal direction, and (2) thereafter, under conditions in which the web is permanently stretchable, stretching the base of the web in a bias direction in a manner that permanently stretches the web base between fastener elements, increasing the spacing of the fastener elements and orienting the rows of fastener elements in a direction diagonal to the machine direction, such that the elements face in a diagonal direction.
In another aspect of the invention, a method of producing a laminated sheet-form product having fastener elements comprises (1) forming from synthetic resin a running web having a multiplicity of discrete fastener elements integral with a base of the web and protruding from one side of the web base in a pattern, (2) thereafter, under conditions in which the web base is permanently stretchable, stretching the web base widthwise to a wider width in a manner that permanently stretches the web base between fastener elements and increases the widthwise spacing of the fastener elements while substantially maintaining the longitudinal spacing of the fastener elements, and (3) bonding an added material to the oppositely directed side of the web base.
In some embodiments the bonding comprises passing the added material and web over a roller under conditions in which the web base is heat-softened.
In other embodiments, the bonding comprises applying an adhesive to either the added material, or the web base, or both, and directing the added material and web to join to form a laminate.
In yet other embodiments, the bonding comprises heat-softening a surface of the added material, and passing the added material and web over a roller such that the web base adheres to the heat-softened surface of the added material.
In the preferred arrangement, the bonding includes forcing the added material and web together such that the web base adheres to the heat-softened surface of the added material, sometimes by forcing the added material and web together against a roller by air pressure.
In another aspect of the invention, a method of producing a sheet-form fastener product comprises (1) forming from synthetic resin a running web having a multiplicity of discrete fastener elements integral with the web and protruding from at least one side of the web in a pattern, the forming causing the molecular structure of the web to be pre-oriented in a longitudinal direction, and (2) thereafter, under conditions in which the web is permanently stretchable, stretching the web widthwise in a manner that permanently stretches the web between fastener elements and increases the widthwise spacing of the fastener elements while substantially maintaining the longitudinal spacing of the fastener elements.
In another aspect of the invention, a fastener product is comprised of synthetic resin and has multiple rows of fastener elements oriented in a first direction along a web base. The web portions between the rows of elements have molecular orientation at a substantial angle to the first direction.
In a preferred arrangement, the fastener elements comprise hook elements with profiles set at a bias direction relative to the running length of the web.
In some cases the web base, in a stretched condition, comprises a thermoplastic film of thickness less than 0.003 inch. In certain cases, the product is adhered to a non-planar surface of a useful product, the film web conforming to the non-planar surface.
In some useful embodiments, the product has a width of eight feet or more.
In certain advantageous examples, the product has molecular orientation in the widthwise direction, providing tear resistance in the lengthwise direction. In certain key embodiments, the product also has molecular orientation in the lengthwise direction, providing tear resistance in the widthwise direction.
In another set of embodiments, a decorative covering comprises the product and a sheet material in a laminated state, the fastener elements of the product providing a means to secure the covering in a desired position. In some instances, the decorative covering comprises a wall covering. In other instances, it comprises a floor covering.
In another aspect of the invention, a machine for forming a fastener product has a pair of rolls forming a nip, at least one of the rolls being a mold roll for forming touch fastener elements integral with a side surface of a running length of a web base. The machine also includes means for supplying plastic resin to the nip, whereby the resin is longitudinally stretched before being molded, and a widthwise stretching device arranged to stretch the web base of an intermediate product produced by the pair of rolls in a direction transverse to the running length of the web base.
In the presently preferred embodiment, the machine includes a heating tunnel through which the intermediate product is passed prior to the stretching device. The heating tunnel is arranged to predominantly heat a side surface of the web base opposite to the side surface on which the fastening elements are disposed.
In a particularly useful embodiment, the means for supplying plastic resin comprises an extruder and the supplied resin is longitudinally stretched by tension caused by the driven rolls, thereby pre-orienting the molecular structure of the resin in the machine direction before forming.
In another configuration, the means for supplying plastic resin comprises an extruder positionable above the nip, and the supplied resin is longitudinally stretched at least partially by gravity forces as it falls from the extruder to the nip.
In another useful arrangement, the machine also includes means for laminating an added material to the stretched web base. In a preferred embodiment, the means for laminating includes a roller about which the product is trained in a stretched condition.
Another aspect of the invention is the use of certain materials and process conditions in the stretching methods described. Advantageously the resin used in the methods comprises a thermoplastic resin having a flex modulus of at least 150,000 pounds per square inch, preferably the thermoplastic resin comprising a material selected from the group consisting of PET, polypropylene, and copolymers of PET and polypropylene. and preferably, in applications requiring high fastener performance, the resin has a flex modulus of at least 250,000 pounds per square inch.
Preferably the thermoplastic resin has an intrinsic viscosity between about 0.6 and 1.1 deciliters per gram, and more preferably the resin has an intrinsic viscosity between about 0.8 and 1.0 deciliters per gram.
In important applications the thermoplastic resin is bottle grade PET, and in certain instances the PET is comprised at least in part of recycled resin.
It is advantageous that the resin comprise a thermoplastic resin having a glass transition temperature of at least 30 degrees Celsius.
Likewise, in cases in which the resin of the web is PET or copolymers thereof, the web is at a temperature between about 90xc2x0 and 120xc2x0 C. during stretching.
Another aspect of the invention features a fastener product comprised of synthetic resin and having multiple rows of fastener elements extending in a first direction along a running web base upon which the fastener elements are integrally molded, the web portions between the rows of elements having molecular orientation at an angle to the first direction as a result of the product having been stretched, after molding, to a width of at least twice its as-molded width.
Another aspect of the invention features a fastener product comprised of synthetic resin and having a multiplicity of rows of molded fastener elements extending along a running web base upon which the fastener elements are integrally molded, the web base between the rows of elements having a degree of molecular orientation in a first direction as a result of being stretched prior to molding, and a degree of molecular orientation in a second direction, perpendicular to the first direction, as a result of being permanently stretched after molding.
Products according to these aspects have one or more of the following features.
The resin comprises a thermoplastic resin having a flex modulus of at least 150,000 pounds per square inch.
The resin comprises an element selected from the group consisting of PET, polypropylene, and copolymers thereof.
The resin comprises a thermoplastic resin having a flex modulus of at least 250,000 pounds per square inch.
The resin comprises a thermoplastic resin having a glass transition temperature of at least 30 degrees Celsius.